Inhibition of Mitochondrial Permeability Transition Enhances Isoflurane-Induced Cardioprotection During Early Reperfusion: The Role of Mitochondrial KATP Channels

Pharmacology of Catechins in Ischemia-Reperfusion Injury of the Heart

Catechins represent a group of polyphenols that possesses various beneficial effects in the cardiovascular system, including protective effects in cardiac ischemia-reperfusion (I/R) injury, a major pathophysiology associated with ischemic heart disease, myocardial infarction, as well as with cardioplegic arrest during heart surgery. In particular, catechin, (−)-epicatechin, and epigallocatechin gallate (EGCG) have been reported to prevent cardiac myocytes from I/R-induced cell damage and I/R-associated molecular changes, finally, resulting in improved cell viability, reduced infarct size, and improved recovery of cardiac function after ischemic insult, which has been widely documented in experimental animal studies and cardiac-derived cell lines. Cardioprotective effects of catechins in I/R injury were mediated via multiple molecular mechanisms, including inhibition of apoptosis; activation of cardioprotective pathways, such as PI3K/Akt (RISK) pathway; and inhibition of stress-associated pathways, including JNK/p38-MAPK; preserving mitochondrial function; and/or modulating autophagy. Moreover, regulatory roles of several microRNAs, including miR-145, miR-384-5p, miR-30a, miR-92a, as well as lncRNA MIAT, were documented in effects of catechins in cardiac I/R. On the other hand, the majority of results come from cell-based experiments and healthy small animals, while studies in large animals and studies including comorbidities or co-medications are rare. Human studies are lacking completely. The dosages of compounds also vary in a broad scale, thus, pharmacological aspects of catechins usage in cardiac I/R are inconclusive so far. Therefore, the aim of this focused review is to summarize the most recent knowledge on the effects of catechins in cardiac I/R injury and bring deep insight into the molecular mechanisms involved and dosage-dependency of these effects, as well as to outline potential gaps for translation of catechin-based treatments into clinical practice.

Mitochondria and Pharmacologic Cardiac Conditioning-At the Heart of Ischemic Injury

Pharmacologic cardiac conditioning increases the intrinsic resistance against ischemia and reperfusion (I/R) injury. The cardiac conditioning response is mediated via complex signaling networks. These networks have been an intriguing research field for decades, largely advancing our knowledge on cardiac signaling beyond the conditioning response. The centerpieces of this system are the mitochondria, a dynamic organelle, almost acting as a cell within the cell. Mitochondria comprise a plethora of functions at the crossroads of cell death or survival. These include the maintenance of aerobic ATP production and redox signaling, closely entwined with mitochondrial calcium handling and mitochondrial permeability transition. Moreover, mitochondria host pathways of programmed cell death impact the inflammatory response and contain their own mechanisms of fusion and fission (division). These act as quality control mechanisms in cellular ageing, release of pro-apoptotic factors and mitophagy. Furthermore, recently identified mechanisms of mitochondrial regeneration can increase the capacity for oxidative phosphorylation, decrease oxidative stress and might help to beneficially impact myocardial remodeling, as well as invigorate the heart against subsequent ischemic insults. The current review highlights different pathways and unresolved questions surrounding mitochondria in myocardial I/R injury and pharmacological cardiac conditioning.

Dexmedetomidine Provides Cardioprotection During Early or Late Reperfusion Mediated by Different Mitochondrial K+-Channels

BACKGROUND

Cardioprotective interventions-such as pharmacological postconditioning-are a promising strategy to reduce deleterious consequences of ischemia and reperfusion injury (I/RI) in the heart, especially as timing and onset of myocardial infarction are unpredictable. Pharmacological postconditioning by treatment with dexmedetomidine (Dex), an α2-adrenoreceptor agonist, during reperfusion protects hearts from I/RI, independently of time point and duration of application during the reperfusion phase. The mitochondrial ATP-sensitive K (mKATP) and mitochondrial large-conductance calcium-sensitive potassium channel (mBKCa) play a pivotal role in mediating this cardioprotective effect. Therefore, we investigated whether Dex-induced cardioprotection during early or late reperfusion is mediated variously by these mitochondrial K-channels.

METHODS

Hearts of male Wistar rats were randomized into 8 groups and underwent a protocol of 15 minutes adaption, 33 minutes ischemia, and 60 minutes reperfusion in an in vitro Langendorff-system. A 10-minute treatment phase was started directly (first subgroup, early reperfusion) or 30 minutes (second subgroup, late reperfusion) after the onset of reperfusion. Control (Con) hearts received vehicle only. In the first subgroup, hearts were treated with 3 nM Dex, 100 µM mKATP-channel blocker 5-hydroxydecanoate (5HD) or 1 µM mBKCa-channel blocker Paxilline (Pax) alone or with respective combinations (5HD + Dex, Pax + Dex). Hearts of the second subgroup received Dex alone (Dex30') or in combination with the respective blockers (5HD + Dex30', Pax + Dex30'). Infarct size was determined with triphenyltetrazoliumchloride staining. Hemodynamic variables were recorded during the whole experiment.

RESULTS

During early reperfusion (first subgroup), the infarct size reducing effect of Dex (Con: 57% ± 9%, Dex: 31% ± 7%; P< .0001 versus Con) was completely abolished by 5HD and Pax (52% ± 6%; Pax + Dex: 53% ± 4%; each P< .0001 versus Dex), while both blockers alone had no effect on infarct size (5HD: 54% ± 8%, Pax: 53% ± 11%). During late reperfusion (second subgroup) the protective effect of Dex (Dex30': 33% ± 10%, P< .0001 versus Con) was fully abrogated by Pax (Pax + Dex30': 58% ± 7%, P < .0001 versus Dex30'), whereas 5HD did not block cardioprotection (5HD + Dex30': 36% ± 7%). Between groups and within each group throughout reperfusion no significant differences in hemodynamic variables were detected.

CONCLUSIONS

Cardioprotection by treatment with Dex during early reperfusion seems to be mediated by both mitochondrial K-channels, whereas during late reperfusion only mBKCa-channels are involved.

Mitochondrial ion channels as targets for cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often result remain the leading causes of death and disability worldwide. As such, new therapeutic targets need to be discovered to protect the myocardium against acute ischaemia/reperfusion (I/R) injury in order to reduce myocardial infarct (MI) size, preserve left ventricular function and prevent the onset of HF. Mitochondrial dysfunction during acute I/R injury is a critical determinant of cell death following AMI, and therefore, ion channels in the inner mitochondrial membrane, which are known to influence cell death and survival, provide potential therapeutic targets for cardioprotection. In this article, we review the role of mitochondrial ion channels, which are known to modulate susceptibility to acute myocardial I/R injury, and we explore their potential roles as therapeutic targets for reducing MI size and preventing HF following AMI.

Cyclosporine A attenuates apoptosis and necrosis after ischemia-reperfusion-induced renal injury in transiently hyperglycemic rats

Purpose:

To investigate the effects of cyclosporine A on renal ischemia-reperfusion injury during transient hyperglycemia in rats.

Methods:

In a model of ischemia-reperfusion-induced renal injury and transiently induced hyperglycemia by intraperitoneal injection of glucose, 2.5 g.kg-1, Wistar rats were anesthetized with either isoflurane or propofol and received intravenous cyclosporine A, 5 mg.kg-1, five minutes before reperfusion. Comparison groups were isoflurane and propofol sham groups and isoflurane and propofol ischemia-reperfusion-induced renal injury. Renal tubular cell viability was quantitatively assessed by flow cytometry after cell culture and classified as early apoptosis, necrotic cells, and intact cells.

Results:

Early apoptosis was significantly higher in isoflurane and propofol anesthetized animals subjected to renal ischemia-reperfusion injury when compared to both cyclosporine A treated and sham groups. Necrosis percentage was significantly higher in propofol-anesthetized animals subjected to renal ischemia-reperfusion injury. The percentage of intact cells was lower in both, isoflurane and propofol anesthetized animals subjected to renal ischemia-reperfusion injury.

Conclusion:

In a model of ischemia-reperfusion-induced renal injury, cyclosporine A, 5 m.kg-1, administered five minutes before renal reperfusion in rats with acute-induced hyperglycemia under either isoflurano or propofol anesthesia, attenuated early apoptosis and preserved viability in renal tubular cells, regardless of the anesthetic used.

Administration of anabolic steroid during adolescence induces long-term cardiac hypertrophy and increases susceptibility to ischemia/reperfusion injury in adult Wistar rats

Chronic administration of anabolic androgenic steroids (AAS) in adult rats results in cardiac hypertrophy and increased susceptibility to myocardial ischemia/reperfusion (IR) injury. Molecular analyses demonstrated that hyperactivation of type 1 angiotensin II (AT1) receptor mediates cardiac hypertrophy induced by AAS and also induces down-regulation of myocardial ATP-sensitive potassium channel (K_ATP), resulting in loss of exercise-induced cardioprotection. Exposure to AAS during adolescence promoted long-term cardiovascular dysfunctions, such as dysautonomia. We tested the hypothesis that chronic AAS exposure in the pre/pubertal phase increases the susceptibility to myocardial ischemia/reperfusion (IR) injury in adult rats. Male Wistar rats (26day old) were treated with vehicle (Control, n=12) or testosterone propionate (TP) (AAS, 5mgkg^-1 n=12) 5 times/week during 5 weeks. At the end of AAS exposure, rats underwent 23days of washout period and were submitted to euthanasia. Langendorff-perfused hearts were submitted to IR injury and evaluated for mechanical dysfunctions and infarct size. Molecular analysis was performed by mRNA levels of α-myosin heavy chain (MHC), βMHC and brain-derived natriuretic peptide (BNP), ryanodine receptor (RyR2) and sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) by quantitative RT-PCR (qRT-PCR). The expression of AT1 receptor and K_ATP channel subunits (Kir6.1 and SURa) was analyzed by qRT-PCR and Western Blot. NADPH oxidase (Nox)-related reactive oxygen species generation was assessed by spectrofluorimetry. The expression of antioxidant enzymes was measured by qRT-PCR in order to address a potential role of redox unbalance. AAS exposure promoted long-term cardiac hypertrophy characterized by increased expression of βMHC and βMHC/αMHC ratio. Baseline derivative of pressure (dP/dt) was impaired by AAS exposure. Postischemic recovery of mechanical properties was impaired (decreased left ventricle [LV] developed pressure and maximal dP/dt; increased LV end-diastolic pressure and minimal dP/dt) and infarct size was larger in the AAS group. Catalase mRNA expression was significantly decreased in the AAS group. In conclusion, chronic administration of AAS during adolescence promoted long-term pathological cardiac hypertrophy and persistent increase in the susceptibility to myocardial IR injury possible due to disturbances on catalase expression.

Sevoflurane mitigates shedding of hyaluronan from the coronary endothelium, also during ischemia/reperfusion: an ex vivo animal study

Glycosaminoglycan hyaluronan (HA), a major constituent of the endothelial glycocalyx, helps to maintain vascular integrity. Preconditioning the heart with volatile anesthetic agents protects against ischemia/reperfusion injury. We investigated a possible protective effect of sevoflurane on the glycocalyx, especially on HA. The effect of pre-ischemic treatment with sevoflurane (15 minutes at 2% vol/vol gas) on shedding of HA was evaluated in 28 isolated, beating guinea pig hearts, subjected to warm ischemia (20 minutes at 37°C) followed by reperfusion (40 minutes), half with and half without preconditioning by sevoflurane. HA concentration was measured in the coronary effluent. Over the last 20 minutes of reperfusion hydroxyethyl starch (1 g%) was continuously infused and the epicardial transudate collected over the last 5 minutes for measuring the colloid extravasation. Additional hearts were fixed by perfusion after the end of reperfusion for immunohistology and electron microscopy. Sevoflurane did not significantly affect post-ischemic oxidative stress, but strongly inhibited shedding of HA during the whole period, surprisingly even prior to ischemia. Immunohistology demonstrated that heparan sulfates and SDC1 of the glycocalyx were also preserved by sevoflurane. Electron microscopy revealed shedding of glycocalyx caused by ischemia and a mostly intact glycocalyx in hearts exposed to sevoflurane. Coronary vascular permeability of the colloid hydroxyethyl starch was significantly decreased by sevoflurane vs the control. We conclude that application of sevoflurane preserves the coronary endothelial glycocalyx, especially HA, sustaining the vascular barrier against ischemic damage. This may explain beneficial effects associated with clinical use of volatile anesthetics against ischemia/reperfusion injury.

The mechanisms of cardio-protective effects of desflurane and sevoflurane at the time of reperfusion: anaesthetic post-conditioning potentially translatable to humans?

Myocardial conditioning is actually an essential strategy in the management of ischaemia-reperfusion injury. The concept of anaesthetic post-conditioning is intriguing, its action occurring at a pivotal moment (that of reperfusion when ischaemia reperfusion lesions are initiated) where the activation of these cardio-protective mechanisms could overpower the mechanisms leading to ischaemia reperfusion injuries. Desflurane and sevoflurane are volatile anaesthetics frequently used during cardiac surgery. This review focuses on the efficacy of desflurane and sevoflurane administered during early reperfusion as a potential cardio-protective strategy. In the context of experimental studies in animal models and in human atrial tissues in vitro, the mechanisms underlying the cardio-protective effect of these agents and their capacity to induce post-conditioning have been reviewed in detail, underlining the role of reactive oxygen species generation, the activation of the cellular signalling pathways, and the actions on mitochondria along with the translatable actions in humans; this might well be sufficient to set the basis for launching randomized clinical studies, actually needed to confirm this strategy as one of real impact.

Peri-operative anaesthetic myocardial preconditioning and protection - cellular mechanisms and clinical relevance in cardiac anaesthesia

Preconditioning has been shown to reduce myocardial damage caused by ischaemia–reperfusion injury peri-operatively. Volatile anaesthetic agents have the potential to provide myocardial protection by anaesthetic preconditioning and, in addition, they also mediate renal and cerebral protection. A number of proof-of-concept trials have confirmed that the experimental evidence can be translated into clinical practice with regard to postoperative markers of myocardial injury; however, this effect has not been ubiquitous. The clinical trials published to date have also been too small to investigate clinical outcome and mortality. Data from recent meta-analyses in cardiac anaesthesia are also not conclusive regarding intra-operative volatile anaesthesia. These inconclusive clinical results have led to great variability currently in the type of anaesthetic agent used during cardiac surgery. This review summarises experimentally proposed mechanisms of anaesthetic preconditioning, and assesses randomised controlled clinical trials in cardiac anaesthesia that have been aimed at translating experimental results into the clinical setting.

Isoflurane protects the myocardium against ischemic injury via the preservation of mitochondrial respiration and its supramolecular organization

BACKGROUND

Isoflurane has been demonstrated to limit myocardial ischemic injury. This effect is hypothesized to be mediated in part via effects on mitochondria. We investigated the hypothesis that isoflurane maintains mitochondrial respiratory chain functionality, in turn limiting mitochondrial damage and mitochondrial membrane disintegration during myocardial ischemic injury.

METHODS

Mice (9-12 weeks of age) received isoflurane (1.0 minimum alveolar concentration) 36 hours before a 30-minute coronary artery occlusion that was followed by 24 hours of reperfusion. Cardiac mitochondria were isolated at a time point corresponding to 4 hours of reperfusion. 2,3,5-Triphenyltetrazoliumchloride staining was used to determine myocardial infarct size. Mitochondrial respiratory chain functionality was investigated using blue native polyacrylamide gel electrophoresis, as well as specific biochemical assays. Mitochondrial lipid peroxidation was quantified via the formation of malondialdehyde; mitochondrial membrane integrity was assessed by Ca-induced swelling. Protein identification was achieved via liquid chromatography mass spectrometry/mass spectrometry.

RESULTS

Thirty-one mice were studied. Mice receiving isoflurane displayed a reduced myocardial infarct size (P = 0.0011 versus ischemia/reperfusion [I/R]), accompanied by a preserved activity of respiratory complex III (P = 0.0008 versus I/R). Isoflurane stabilized mitochondrial supercomplexes consisting of oligomers from complex III/IV (P = 0.0086 versus I/R). Alleviation of mitochondrial damage after isoflurane treatment was further demonstrated as decreased malondialdehyde formation (P = 0.0019 versus I/R) as well as a diminished susceptibility to Ca-induced swelling (P = 0.0010 versus I/R).

CONCLUSIONS

Our findings support the hypothesis that isoflurane protects the heart from ischemic injury by maintaining the in vivo functionality of the mitochondrial respiratory chain. These effects may result in part from the preservation of mitochondrial supramolecular organization and minimized oxidative damage, circumventing the loss of mitochondrial membrane integrity.

Cardioprotective trafficking of caveolin to mitochondria is Gi-protein dependent

BACKGROUND

Caveolae are a nexus for protective signaling. Trafficking of caveolin to mitochondria is essential for adaptation to cellular stress though the trafficking mechanisms remain unknown. The authors hypothesized that G protein-coupled receptor/inhibitory G protein (Gi) activation leads to caveolin trafficking to mitochondria.

METHODS

Mice were exposed to isoflurane or oxygen vehicle (30 min, ± 36 h pertussis toxin pretreatment, an irreversible Gi inhibitor). Caveolin trafficking, cardioprotective "survival kinase" signaling, mitochondrial function, and ultrastructure were assessed.

RESULTS

Isoflurane increased cardiac caveolae (n = 8 per group; data presented as mean ± SD for Ctrl versus isoflurane; [caveolin-1: 1.78 ± 0.12 vs. 3.53 ± 0.77; P < 0.05]; [caveolin-3: 1.68 ± 0.29 vs. 2.67 ± 0.46; P < 0.05]) and mitochondrial caveolin levels (n = 16 per group; [caveolin-1: 0.87 ± 0.18 vs. 1.89 ± .19; P < 0.05]; [caveolin-3: 1.10 ± 0.29 vs. 2.26 ± 0.28; P < 0.05]), and caveolin-enriched mitochondria exhibited improved respiratory function (n = 4 per group; [state 3/complex I: 10.67 ± 1.54 vs. 37.6 ± 7.34; P < 0.05]; [state 3/complex II: 37.19 ± 4.61 vs. 71.48 ± 15.28; P < 0.05]). Isoflurane increased phosphorylation of survival kinases (n = 8 per group; [protein kinase B: 0.63 ± 0.20 vs. 1.47 ± 0.18; P < 0.05]; [glycogen synthase kinase 3β: 1.23 ± 0.20 vs. 2.35 ± 0.20; P < 0.05]). The beneficial effects were blocked by pertussis toxin.

CONCLUSIONS

Gi proteins are involved in trafficking caveolin to mitochondria to enhance stress resistance. Agents that target Gi activation and caveolin trafficking may be viable cardioprotective agents.

Mitochondrial targets for volatile anesthetics against cardiac ischemia-reperfusion injury

Mitochondria are critical modulators of cell function and are increasingly recognized as proximal sensors and effectors that ultimately determine the balance between cell survival and cell death. Volatile anesthetics (VA) are long known for their cardioprotective effects, as demonstrated by improved mitochondrial and cellular functions, and by reduced necrotic and apoptotic cell death during cardiac ischemia and reperfusion (IR) injury. The molecular mechanisms by which VA impart cardioprotection are still poorly understood. Because of the emerging role of mitochondria as therapeutic targets in diseases, including ischemic heart disease, it is important to know if VA-induced cytoprotective mechanisms are mediated at the mitochondrial level. In recent years, considerable evidence points to direct effects of VA on mitochondrial channel/transporter protein functions and electron transport chain (ETC) complexes as potential targets in mediating cardioprotection. This review furnishes an integrated overview of targets that VA impart on mitochondrial channels/transporters and ETC proteins that could provide a basis for cation regulation and homeostasis, mitochondrial bioenergetics, and reactive oxygen species (ROS) emission in redox signaling for cardiac cell protection during IR injury.

Postconditioning with sevoflurane protects against focal cerebral ischemia and reperfusion injury involving mitochondrial ATP-dependent potassium channel and mitochondrial permeability transition pore

OBJECTIVES

Postconditioning with sevoflurane has been shown to protect against focal cerebral ischemia and reperfusion injury. However, the mechanism remains elusive. In this study, we tested the hypothesis that mitochondrial ATP-sensitive potassium (mitoKATP) and mitochondrial permeability transition pore (mPTP) play roles in the neuroprotection of postconditioning with sevoflurane.

METHODS

Adult male Sprague-Dawley rats were subjected to MCAO for 90 minutes and then treated with sevoflurane at the beginning of reperfusion. The infarct volume, neurological deficit score, and brain edema were evaluated at 24 hours. Apoptosis were studied by TUNEL. The neuroprotective effect with or without 5-hydroxydecanoate (5-HD), a selective mitoKATP channel blocker or atractyloside (ATR), and an mPTP opener were analyzed.

RESULTS

Postconditioning with sevoflurane significantly decreased neurological deficit scores, infarct volume, and brain edema and also reduced apoptotic cells. 5-HD and ATR abolished the neuroprotective effect, respectively. 5-HD or ATR alone had no effect on ischemia and reperfusion injury.

DISCUSSION

Our data suggest that mitoKATP and mPTP play crucial roles in the neuroprotection of postconditioning with sevoflurane.

Cellular mechanisms against ischemia reperfusion injury induced by the use of anesthetic pharmacological agents

Ischemia-reperfusion (IR) cycle in the myocardium is associated with activation of an injurious cascade, thus leading to new myocardial challenges, which account for up to 50% of infarct size. Some evidence implicates reactive oxygen species (ROS) as a probable cause of myocardial injury in prooxidant clinical settings. Damage occurs during both ischemia and post-ischemic reperfusion in animal and human models. The mechanisms that contribute to this damage include the increase in cellular calcium (Ca(2+)) concentration and induction of ROS sources during reperfusion. Pharmacological preconditioning, which includes pharmacological strategies that counteract the ROS burst and Ca(2+) overload followed to IR cycle in the myocardium, could be effective in limiting injury. Currently widespread evidence supports the use of anesthetics agents as an important cardioprotective strategy that act at various levels such as metabotropic receptors, ion channels or mitochondrial level. Their administration before a prolonged ischemic episode is known as anesthetic preconditioning, whereas when given at the very onset of reperfusion, is termed anesthetic postconditioning. Both types of anesthetic conditioning reduce, albeit not to the same degree, the extent of myocardial injury. This review focuses on cellular and pathophysiological concepts on the myocardial damage induced by IR and how anesthetic pharmacological agents commonly used could attenuate the functional and structural effects induced by oxidative stress in cardiac tissue.

Isoflurane reduces hypoxia/reoxygenation-induced apoptosis and mitochondrial permeability transition in rat primary cultured cardiocytes

Background

The volatile anesthetic isoflurane protects the heart from hypoxia/reperfusion (H/R) injury. However, it is still incompletely understood whether isoflurane exerts its protective role through preventing mitochondrial permeability transition pore (MPTP) opening.

Methods

Primary cultured cardiocytes were exposed to H/R in the absence or presence of isoflurane. Cell cytotoxicity and apoptosis were detected by MTT assay and TUNEL staining, respectively. MPTP function was monitored by confocal imaging after reoxygenation. ROS production and activation of caspase-3 were determined by fluorescent reader and western blot, respectively.

Results

As compared to the control group, H/R led to significant cell cytotoxicity and apoptosis, while application of isoflurane markedly reversed the effects. Furthermore, isoflurane significantly inhibits the formation of H/R-induced excess ROS production. Finally, isoflurane attenuated the onset of mitochondrial permeability transition pore (MPTP) occurred during hypoxia/reoxygenation, and in turn inhibited activation of caspase-3.

Conclusions

These data indicate that isoflurane has a protective effect on cardiocytes exposed to H/R by reducing excess ROS production, blocking open of MPTP and further reducing apoptosis.

Cellular signaling pathways and molecular mechanisms involving inhalational anesthetics-induced organoprotection

Inhalational anesthetics-induced organoprotection has received much research interest and has been consistently demonstrated in different models of organ damage, in particular, ischemia-reperfusion injury, which features prominently in the perioperative period and in cardiovascular events. The cellular mechanisms accountable for effective organoprotection over heart, brain, kidneys, and other vital organs have been elucidated in turn in the past two decades, including receptor stimulations, second-messenger signal relay and amplification, end-effector activation, and transcriptional modification. This review summarizes the signaling pathways and the molecular participants in inhalational anesthetics-mediated organ protection published in the current literature, comparing and contrasting the 'preconditioning' and 'postconditioning' phenomena, and the similarities and differences in mechanisms between organs. The salubrious effects of inhalational anesthetics on vital organs, if reproducible in human subjects in clinical settings, would be of exceptional clinical importance, but clinical studies with better design and execution are prerequisites for valid conclusions to be made. Xenon as the emerging inhalational anesthetic, and its organoprotective efficacy, mechanism, and relative advantages over other anesthetics, are also discussed.

The effect of prethrombolytic cyclosporine-A injection on clinical outcome of acute anterior ST-elevation myocardial infarction

INTRODUCTION

Reperfusion injury reduces the benefits of early reperfusion therapies after acute ST-elevation myocardial infarction (STEMI). Cyclosporine-A (CsA) is a potent inhibitor of opening of the mitochondrial permeability transition pore, which has been shown to play a key role in myocardial reperfusion injury. The impact of this treatment on clinical outcomes of acute STEMI remains unknown. Our aim was to investigate the clinical outcomes of using this drug in patients with acute anterior STEMI receiving thrombolytic treatment (TLT).

METHODS

In this double-blinded randomized clinical trial, 101 patients with acute anterior STEMI who were candidate for TLT, were enrolled and randomly assigned into treatment or control groups. Patients in the treatment group received an intravenous bolus injection of 2.5 mg/kg of CsA immediately before TLT. The patients in the control group received an equivalent volume of normal saline. Infarct size, occurrence of major arrhythmias, heart failure, left ventricular ejection fraction (LVEF), TLT-related complications, in-hospital and 6-month mortality rates were investigated.

RESULTS

There were no significant differences among the demographics, myocardial enzyme release, occurrence of major arrhythmias [9 (18%) vs. 12 (23.5%), P = 0.80], heart failure [18 (36%) vs. 19 (38.3%), P = 0.83], LVEF at first day [34.7 ± 9.9% vs. 33.5 ± 8.1%, P = 0.50] or at discharge [37.7 ± 10% vs. 36.1 ± 8.2%, P = 0.43], and in-hospital [4 (8%) vs. 6 (11.8%), P = 0.74] or 6-month mortality rates [9 (18%) vs. 10 (19.6%), P = 0.99] between the CsA vs. the control group.

CONCLUSION

In this study, the prethrombolytic administration of CsA was not associated with a reduction in the infarct size or any improvement in clinical outcomes.

Cardioprotection against myocardial reperfusion injury: successes, failures, and perspectives

The past few decades have witnessed an enormous number of research strategies aimed at protecting the heart against myocardial ischemia-reperfusion injury. Several randomized clinical trials are nowadays in progress testing whether promising therapeutic strategies aimed at preventing lethal reperfusion injury can be translated from bench to bedside. Many of these interventions, either pharmacological or mechanical, are targeting mitochondria as the final effectors of cardioprotection. Despite encouraging pre-clinical studies and small proof of concept clinical trials, there are still several limitations that may jeopardize the efficacy of cardioprotective strategies. These limitations include clinical setting, patient profile, drug administration, and methods for evaluating treatment efficacy. Identifying potential mechanistic and methodological pitfalls in the field may improve future translational research.

Emulsified isoflurane postconditioning produces cardioprotection against myocardial ischemia-reperfusion injury in rats

Emulsified isoflurane (EIso) preconditioning can induce cardioprotection. We investigated whether EIso application after ischemia protects hearts against reperfusion injury and whether it is mediated by the inhibition of apoptosis. Rats were subjected to 30-min coronary occlusion followed by 180-min reperfusion. At the onset of reperfusion, rats were intravenously administered saline (sham, control group), 30 % intralipid (IL group) or 2 ml kg(-1) EIso (EIso group) for 30 min. After reperfusion, infarct sizes, myocardial apoptosis and expression of Bcl-2, Bax and caspase-3 proteins were determined. Hemodynamic parameters were not different among groups. Compared with control and intralipid group, EIso limited infarct size, inhibited apoptosis, increased the expression of Bcl-2, decreased the expression of Bax, cleaved caspase-3, and enhanced Bcl-2/Bax ratio. EIso protects hearts against reperfusion injury when administered at the onset of reperfusion, which may be mediated by the inhibition of apoptosis via modulation of the expression of pro- and anti-apoptotic proteins.

Sevoflurane preconditioning improves mitochondrial function and long-term neurologic sequelae after transient cerebral ischemia: role of mitochondrial permeability transition

OBJECTIVE

Anesthetic preconditioning appears to be a viable strategy to treat ischemic cerebral injury. Here we investigated 1) whether the protection conferred by sevoflurane preconditioning sustains in time; 2) whether sevoflurane preconditioning diminishes mitochondrial dysfunction following cerebral ischemia; and 3) whether mitochondrial permeability transition pore plays a crucial role in the sevoflurane preconditioning.

DESIGN

Laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

: Sprague-Dawley rats.

INTERVENTIONS

Rats underwent 2 hrs of focal cerebral ischemia induced by middle cerebral artery occlusion. Preconditioning was elicited with sevoflurane (2.3%) for 60 mins at 24 hrs before ischemia. The involvement of mitochondrial permeability transition pore was determined with a mitochondrial permeability transition pore opener atractyloside and a specific mitochondrial permeability transition pore inhibitor cyclosporin A. In vitro study was performed on acutely isolated mitochondria subjected to calcium overload.

MEASUREMENTS AND MAIN RESULTS

Sevoflurane preconditioning significantly decreased the infarct size by 35.9% (95% confidence interval 6.5-28.4, p < .001). This reduction of injury volume was associated with a long-term improvement of neurological function according to modified neurological severity score (F = 13.6, p = .001) and sticky-tape test (F = 29.1, p < .001) for 42 days after ischemia. Furthermore, sevoflurane preconditioning markedly protected mitochondria, as indicated by preserved respiratory chain complex activities and membrane potential, lowered mitochondrial hydrogen-peroxide production, and attenuated mitochondrial permeability transition pore opening. Isolated mitochondria also demonstrated a reduced sensitivity to Ca-induced mitochondrial permeability transition pore opening after pre-exposure to sevoflurane in vitro (95% confidence interval 24.2-196.5,p = .006). Inhibiting mitochondrial permeability transition pore using cyclosporin A resulted in protective effects similar to those seen with sevoflurane preconditioning, whereas pharmacologically opening the mitochondrial permeability transition pore with atractyloside abrogated all the positive effects of sevoflurane preconditioning and cyclosporin A, including suppression of mitochondrial permeability transition pore opening, counteraction of mitochondria-dependent apoptotic pathway, and subsequent histological and behavioral improvements.

CONCLUSIONS

Sevoflurane preconditioning protects mitochondria from cerebral ischemia/reperfusion injury and ameliorates long-term neurological deficits. Inhibition of mitochondrial permeability transition pore opening is a crucial step in mediating the neuroprotection of sevoflurane preconditioning.

Skeletal muscle post-conditioning by diazoxide, anti-oxidative and anti-apoptotic mechanisms

Pretreatment with diazoxide, K(ATP) channel opener, increases tissue tolerance against ischemia reperfusion (IR) injury. In clinical settings pretreatment is rarely an option therefore we evaluated the effect of post-ischemic treatment with diazoxide on skeletal muscle IR injury. Rats were treated with either saline, diazoxide (K(ATP) opener; 40 mg/kg) or 5-hydroxydecanoate (5-HD; mitochondrial K(ATP) inhibitor; 40 mg/kg) after skeletal muscle ischemia (3 h) and reperfusion (6, 24 or 48 h). Tissue contents of malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) activities, Bax and Bcl-2 protein expression and muscle histology were determined. Apoptosis was examined (24 and 48 h) after ischemia. IR induced severe histological damage, increased MDA content and Bax expression (24 and 48 h; p < 0.01) and decreased CAT and SOD activities (6 and 24 h, p < 0.01 and 48 h, p < 0.05), with no significant effect on Bcl-2 expression. Diazoxide reversed IR effects on MDA (6 and 24 h; p < 0.05), SOD (6 and 24 h; p < 0.01) and CAT (6 and 48 h, p < 0.05 and 24 h p < 0.01) and tissue damage. Diazoxide also decreased Bax (24 and 48 h; p < 0.05) and increased Bcl-2 protein expression (24 and 48 h; p < 0.01). Post-ischemic treatment with 5-HD had no significant effect on IR injury. Number of apoptotic nuclei in IR and 5-HD treated groups significantly increased (p < 0.001) while diazoxide decreased apoptosis (p < 0.01). The results suggested that post-ischemic treatment with diazoxide decrease oxidative stress in acute phase which modulates expression of apoptotic proteins in the late phase of reperfusion injury. Involvement of KATP channels in this effect require further evaluations.

Complex I and ATP synthase mediate membrane depolarization and matrix acidification by isoflurane in mitochondria

Short application of the volatile anesthetic isoflurane at reperfusion after ischemia exerts strong protection of the heart against injury. Mild depolarization and acidification of the mitochondrial matrix are involved in the protective mechanisms of isoflurane, but the molecular basis for these changes is not clear. In this study, mitochondrial respiration, membrane potential, matrix pH, matrix swelling, ATP synthesis and -hydrolysis, and H(2)O(2) release were assessed in isolated mitochondria. We hypothesized that isoflurane induces mitochondrial depolarization and matrix acidification through direct action on both complex I and ATP synthase. With complex I-linked substrates, isoflurane (0.5mM) inhibited mitochondrial respiration by 28 ± 10%, and slightly, but significantly depolarized membrane potential and decreased matrix pH. With complex II- and complex IV-linked substrates, respiration was not changed, but isoflurane still decreased matrix pH and depolarized mitochondrial membrane potential. Depolarization and matrix acidification were attenuated by inhibition of ATP synthase with oligomycin, but not by inhibition of mitochondrial ATP- and Ca(2+)-sensitive K(+) channels or uncoupling proteins. Isoflurane did not induce matrix swelling and did not affect ATP synthesis and hydrolysis, but decreased H(2)O(2) release in the presence of succinate in an oligomycin- and matrix pH-sensitive manner. Isoflurane modulated H(+) flux through ATP synthase in an oligomycin-sensitive manner. Our results indicate that isoflurane-induced mitochondrial depolarization and acidification occur due to inhibition of the electron transport chain at the site of complex I and increased proton flux through ATP synthase. K(+) channels and uncoupling proteins appear not to be involved in the direct effects of isoflurane on mitochondria.

Cyclosporin variably and inconsistently reduces infarct size in experimental models of reperfused myocardial infarction: a systematic review and meta-analysis

Cyclosporin is an immunosuppressant that has recently been proposed as a treatment to prevent reperfusion injury in acute myocardial infarction (MI). We aimed to determine the overall efficacy of cyclosporin in experimental studies of acute reperfused MI. We conducted a systematic review and stratified meta-analysis of published studies describing the efficacy of cyclosporin in experimental models of acute reperfused MI. We included all in vivo publications of cyclosporin where infarct size was measured. A literature search identified 29 potential studies of which 20 fulfilled the eligibility criteria. In these studies (involving four species of animals), cyclosporin reduced myocardial infarct size by a standardized mean (95% confidence interval) difference of -1.60 (-2.17, -1.03) compared with controls. Cyclosporin failed to demonstrate a convincing benefit in studies involving pigs. Despite this observation, the overall efficacy of cyclosporin did not differ across species (P= 0.358). The dose of cyclosporin given did not affect final infarct size (P= 0.203). Funnel plots of these data suggested heterogeneity among the studies. Cyclosporin had variable effects on infarct size compared with placebo. Cyclosporin had no effect on myocardial infarct size in swine, raising a question over the potential cardioprotective effects of cyclosporin in man.

High-dose fasudil preserves postconditioning against myocardial infarction under hyperglycemia in rats: role of mitochondrial KATP channels

BACKGROUND

The current study was carried out to determine whether fasudil hydrochloride (fasudil), a Rho-kinase inhibitor, has myocardial postconditioning (PostC) activity under hyperglycemia as well as normoglycemia, and if so, whether the effects could be mediated by mitochondrial ATP-sensitive potassium (m-KATP) channels.

METHODS

Male Sprague-Dawley rats were anesthetized with sodium pentobarbital. After opening the chest, all rats underwent 30-min coronary artery occlusion followed by 2-h reperfusion. The rats received low-dose (0.15 mg/kg) or high-dose (0.5 mg/kg) fasudil or diazoxide, an m-KATP channel opener, at 10 mg/kg, just before reperfusion under normoglycemic or hyperglycemic conditions. In another group, rats received 5-hydroxydecanoic acid (5HD), an m-KATP channel blocker, at 10 mg/kg, before high-dose fasudil. Myocardial infarct size was expressed as a percentage of area at risk (AAR).

RESULTS

Under normoglycemia, low-dose and high-dose fasudil and diazoxide reduced myocardial infarct size (23 ± 8%, 21 ± 9% and 21 ± 10% of AAR, respectively) compared with that in the control (42 ± 7%). Under hyperglycemia, low-dose fasudil (40 ± 11%) and diazoxide (44 ± 14%) could not exert this beneficial effect, but high-dose fasudil reduced myocardial infarct size in the same manner as under normoglycemia (21 ± 13%). 5HD prevented fasudil-induced reduction of myocardial infarct size (42 ± 13%).

CONCLUSION

Fasudil induces PostC against myocardial infarction via activation of m-KATP channels in the rat. Although hyperglycemia attenuates the PostC, high-dose fasudil can restore cardioprotection.

The mitochondrial permeability transition pore and its role in anaesthesia-triggered cellular protection during ischaemia-reperfusion injury

This review summarises the most recent data in support of the role of the mitochondrial permeability transition pore (mPTP) in ischaemia-reperfusion injury, how anaesthetic agents interact with this molecular channel, and the relevance this holds for current anaesthetic practice. Ischaemia results in damage to the electron transport chain of enzymes and sets into play the assembly of a non-specific mega-channel (the mPTP) that transgresses the inner mitochondrial membrane. During reperfusion, uncontrolled opening of the mPTP causes widespread depolarisation of the inner mitochondrial membrane, hydrolysis of ATP, mitochondrial rupture and eventual necrotic cell death. Similarly, transient opening of the mPTP during less substantial ischaemia leads to differential swelling of the intermembrane space compared to the mitochondrial matrix, rupture of the outer mitochondrial membrane and release of pro-apoptotic factors into the cytosol. Recent data suggests that cellular protection from volatile anaesthetic agents follows specific downstream interactions with this molecular channel that are initiated early during anaesthesia. Intravenous anaesthetic agents also prevent the opening of the mPTP during reperfusion. Although by dissimilar mechanisms, both volatiles and propofol promote cell survival by preventing uncontrolled opening of the mPTP after ischaemia. It is now considered that anaesthetic-induced closure of the mPTP is the underlying effector mechanism that is responsible for the cytoprotection previously demonstrated in clinical studies investigating anaesthetic-mediated cardiac and neuroprotection. Manipulation of mPTP function offers a novel means of preventing ischaemic cell injury. Anaesthetic agents occupy a unique niche in the pharmacological armamentarium available for use in preventing cell death following ischaemia-reperfusion injury.

Desflurane-induced post-conditioning against myocardial infarction is mediated by calcium-activated potassium channels: role of the mitochondrial permeability transition pore

BACKGROUND

Desflurane (DES)-induced preconditioning is mediated by large-conductance calcium-activated potassium channels (BK(Ca)). Whether BK(Ca) are involved in anaesthetic-induced post-conditioning is unknown. We tested the hypothesis that DES-induced post-conditioning is mediated by BK(Ca) upstream of the mitochondrial permeability transition pore (mPTP).

METHODS

Pentobarbital-anaesthetized male C57Black/6 mice were subjected to 45 min coronary artery occlusion (CAO) and 3 h reperfusion. Animals received either no intervention or dimethylsulphoxide (DMSO, 10 µl g(-1)). DES (1.0 MAC, 7.5 vol%) was administered for 18 min, starting 3 min before the end of CAO. The following agents were given either alone or in combination with DES: the BK(Ca) activator NS1619 (1 µg g(-1)), the BK(Ca) inhibitor iberiotoxin (IbTx, 0.05 µg g(-1)), the mPTP opener atractyloside (ATRA, 25 µg g(-1)), and the mPTP inhibitor cyclosporine A (CYC A, 10 µg g(-1)). Infarct size (IS) was determined with triphenyltetrazolium chloride and the area at risk with Evans Blue, respectively.

RESULTS

IS in control animals was 48(6)%. Neither DMSO, IbTx nor ATRA affected myocardial IS. DES alone or NS1619 alone or the combination reduced IS (P<0.05), CYC A alone or in combination with IbTx or DES also reduced IS (P<0.05). DES-induced reduction of myocardial IS was completely abolished by IbTx and was partially blocked by ATRA and ATRA partially blocked IS reduction by NS1619.

CONCLUSIONS

These data suggest that DES-induced post-conditioning against myocardial infarction is mediated by BK(Ca) and mPTP. Cardioprotection by BK(Ca) activator NS1619 might occur, at least in part, independently of mPTP.

Heart rate limitation and cardiac unloading in sevoflurane post-conditioning

BACKGROUND

Sevoflurane post-conditioning (SePost) has been found to alleviate ischemic myocardial reperfusion injury through the activation of prosurvival kinases. Lowered myocardial oxygen demand from reduced cardiac work may also contribute to cardioprotection, and is much less well-studied. Our aim was to examine the simultaneous effects of SePost on cardiac work (here, rate-pressure product, RPP) and myocardial infarct size in a porcine model.

METHODS

Anesthetized 25 kg pigs were randomly allocated to two groups and underwent 45 min regional coronary artery balloon occlusion and subsequent 2 h reperfusion. SePost (n = 10) was given as sevoflurane 1.5-3% end-tidal concentration during reperfusion while controls (n = 12) were untreated. Aortic blood pressure was measured directly, while mixed-venous oxygen saturation and cardiac output were measured in the pulmonary artery. Cardiac work was determined as RPP. Post-mortem, histologic myocardial infarct size (IS), and area at risk were determined in transverse heart slices after tetrazolium stain.

RESULTS

Myocardial infarct size was reduced from (control) 55.0 (mean) ± 13.6% (standard deviation) to 32.5 ± 13.4% in group SePost (P = 0.0009). During reperfusion, SePost resulted in lower heart rate (P = 0.0003), cardiac output (P = 0.0123), mixed-venous oxygen saturation (P = 0.0103), blood pressure, and RPP (P < 0.0001). RPP was highly correlated to IS (P = 0.0055).

CONCLUSION

SePost (1.5-3%) reduced infarct size after regional myocardial ischemia in vivo and reduced cardiac work was significantly correlated to myocardial salvage.

Cyclosporine A, 2.5 mg/kg, does not reduce myocardial infarct size in a porcine model of ischemia and reperfusion

BACKGROUND

In recent years, cyclosporine A (CsA) has emerged as a promising therapy to limit myocardial ischemic-reperfusion injury, presumably by inhibiting the opening of the mitochondrial permeability transition pore. Results from different large animal models are conflicting, however, with failure to prove beneficial effects of 10 mg/kg CsA administered at reperfusion. Recently, a small clinical study using a bolus of 2.5 mg/kg CsA showed promising but not unequivocal results. The aim of the present study was to estimate the magnitude of a possible infarct reduction with the use of the latter regimen in a closed-chest porcine model for ischemia and reperfusion. Materials and

METHODS

Pigs underwent catheterization with balloon occlusion of the left descending coronary artery for 40 minutes, followed by reperfusion for 4 hours. They were randomized to receive an intravenous bolus 7 minutes before reperfusion of either 2.5 mg/kg CsA (n = 12) or saline (control, n = 11). Hearts were stained to quantify area at risk and infarct size.

RESULTS

Throughout the experiment, there were no differences between the groups in baseline characteristics or hemodynamic variables. CsA treatment did not reduce infarct size as a proportion of area at risk compared with control (51% ± 6% and 54% ± 6%, respectively, P = .75).

CONCLUSION

In a closed-chest porcine model for myocardial ischemia and reperfusion injury, 2.5 mg/kg CsA administered before reperfusion did not reduce infarct size.

Postconditioning by xenon and hypothermia in the rat heart in vivo

BACKGROUND AND OBJECTIVE

Hypothermia protects against myocardial reperfusion injury. However, inducing hypothermia takes time, which makes it unsuitable as an emergency treatment. Combining mild hypothermia with low-dose xenon, applied either simultaneously or one after the other, protects the neonatal rat brain against reperfusion injury. We investigated whether xenon, administered prior to hypothermia or simultaneously with hypothermia, also protects the rat heart from reperfusion injury.

METHODS

Anaesthetized rats (chloralose, ketamine, diazepam) were randomly allocated to five groups and subjected to 25 min coronary artery occlusion, followed by 120 min reperfusion. At the onset of reperfusion, controls received no intervention and inhaled oxygen in air with an inspired oxygen fraction of 0.8 (Con80). Further groups received either 1 h of mild hypothermia of 34 degrees C (Hypo34) or 30 min of xenon 20% (Xe20). Additional groups received xenon 20% and hypothermia 34 degrees C simultaneously (Xe20 + Hypo34) or in succession (Xe20-->Hypo34). Infarct sizes were assessed by triphenyltetrazolium chloride staining.

RESULTS

The combination of xenon 20% and hypothermia 34 degrees C significantly reduced infarct size [Xe20 + Hypo34: 55(22)%, mean (SD)] compared with control [Con80: 76(12)%, P = 0.03]. Xenon and hypothermia in succession produced no infarct size reduction.

CONCLUSION

The combination of xenon 20% and hypothermia of 34 degrees C, applied during early reperfusion, reduces infarct size in the rat heart in vivo.

Mitochondria in postconditioning

Several signal transduction pathways are activated by cardioprotective stimuli, including ischemic or pharmacological postconditioning. These pathways converge on a common target, the mitochondria, and cardioprotection by postconditioning is associated with preserved mitochondrial function after ischemia/reperfusion. The present review discusses the role of mitochondria in cardioprotection, especially the involvement of ATP-dependent potassium channels, reactive oxygen species, and the mitochondrial permeability transition pore, and focuses on the effects of postconditioning on mitochondrial function (i.e., their oxygen consumption and calcium retention capacity). The contribution of mitochondria to loss of protection by postconditioning in diseased or aged myocardium is also addressed.

Sevoflurane postconditioning reduces myocardial reperfusion injury in rat isolated hearts via activation of PI3K/Akt signaling and modulation of Bcl-2 family proteins

Sevoflurane postconditioning reduces myocardial infarct size. The objective of this study was to examine the role of the phosphatidylinositol-3-kinase (PI3K)/Akt pathway in anesthetic postconditioning and to determine whether PI3K/Akt signaling modulates the expression of pro- and antiapoptotic proteins in sevoflurane postconditioning. Isolated and perfused rat hearts were prepared first, and then randomly assigned to the following groups: Sham-operation (Sham), ischemia/reperfusion (Con), sevoflurane postconditioning (SPC), Sham plus 100 nmol/L wortmannin (Sham+Wort), Con+Wort, SPC+Wort, and Con+dimethylsulphoxide (DMSO). Sevoflurane postconditioning was induced by administration of sevoflurane (2.5%, v/v) for 10 min from the onset of reperfusion. Left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), maximum increase in rate of LVDP (+dP/dt), maximum decrease in rate of LVDP (-dP/dt), heart rate (HR), and coronary flow (CF) were measured at baseline, R30 min (30 min of reperfusion), R60 min, R90 min, and R120 min. Creatine kinase (CK) and lactate dehydrogenase (LDH) were measured after 5 min and 10 min reperfusion. Infarct size was determined by triphenyltetrazolium chloride staining at the end of reperfusion. Total Akt and phosphorylated Akt (phospho-Akt), Bax, Bcl-2, Bad, and phospho-Bad were determined by Western blot analysis. Analysis of variance (ANOVA) and Student-Newman-Keuls' test were used to investigate the significance of differences between groups. The LVDP, + or - dP/dt, and CF were higher and LVEDP was lower in the SPC group than in the Con group at all points of reperfusion (P<0.05). The SPC group had significantly reduced CK and LDH release and decreased infarct size compared with the Con group [(22.9 + or - 8)% vs. (42.4 + or - 9.4)%, respectively; P<0.05]. The SPC group also had increased the expression of phospho-Akt, Bcl-2, and phospho-Bad, and decreased the expression of Bax. Wortmannin abolished the cardioprotection of sevoflurane postconditioning. Sevoflurane postconditioning may protect the isolated rat heart. Activation of PI3K and modulation of the expression of pro- and antiapoptotic proteins may play an important role in sevoflurane-induced myocardial protection.

Bradykinin and adenosine receptors mediate desflurane induced postconditioning in human myocardium: role of reactive oxygen species

BACKGROUND

Desflurane during early reperfusion has been shown to postcondition human myocardium, in vitro. We investigated the role of adenosine and bradykinin receptors, and generation of radical oxygen species in desflurane-induced postconditioning in human myocardium.

METHODS

We recorded isometric contraction of human right atrial trabeculae hanged in an oxygenated Tyrode's solution (34 degrees Celsius, stimulation frequency 1 Hz). After a 30-min hypoxic period, desflurane 6% was administered during the first 5 min of reoxygenation. Desflurane was administered alone or with pretreatment of N-mercaptopropionylglycine, a reactive oxygen species scavenger, 8-(p-Sulfophenyl)theophylline, an adenosine receptor antagonist, HOE140, a selective B2 bradykinin receptor antagonist. In separate groups, adenosine and bradykinin were administered during the first minutes of reoxygenation alone or in presence of N-mercaptopropionylglycine. The force of contraction of trabeculae was recorded continuously. Developed force at the end of a 60-min reoxygenation period was compared (mean +/- standard deviation) between the groups by a variance analysis and post hoc test.

RESULTS

Desflurane 6% (84 +/- 6% of baseline) enhanced the recovery of force after 60-min of reoxygenation as compared to control group (51 +/- 8% of baseline, P < 0.0001). N-mercaptopropionylglycine (54 +/- 3% of baseline), 8-(p-Sulfophenyl)theophylline (62 +/- 9% of baseline), HOE140 (58 +/- 6% of baseline) abolished desflurane-induced postconditioning. Adenosine (80 +/- 9% of baseline) and bradykinin (83 +/- 4% of baseline) induced postconditioning (P < 0.0001 vs control), N-mercaptopropionylglycine abolished the beneficial effects of adenosine and bradykinin (54 +/- 8 and 58 +/- 5% of baseline, respectively).

CONCLUSIONS

In vitro, desflurane-induced postconditioning depends on reactive oxygen species production, activation of adenosine and bradykinin B2 receptors. And, the cardioprotective effect of adenosine and bradykinin administered at the beginning of reoxygenation, was mediated, at least in part, through ROS production.

Signaling pathways involved in postconditioning-induced cardioprotection of human myocardium, in vitro

We examined the respective role and relationship between protein kinase C (PKC), mitochondrial adenosine triphosphate-sensitive potassium (mitoK(ATP)) channel and p38 mitogen-activated protein kinase (MAPK) in postconditioning of human myocardium, in vitro. Isometrically contracting, isolated human right atrial trabeculae were exposed to 30 min hypoxia and 60 min reoxygenation. Phorbol 12-myristate 13-acetate (a PKC activator), diazoxide (a mitoK(ATP) opener) and anisomycin (a p38 MAPK activator) were superfused in early reoxygenation alone and with calphostin C (a PKC inhibitor), 5-hydroxy-decanoate (5-HD, a mitoK(ATP) channel inhibitor) and SB 202190 (a p38 MAPK inhibitor). Developed force at the end of the 60 min reoxygenation (FoC(60)) period was compared between groups (mean +/- SD). Phorbol 12-myristate 13-acetate (91 +/- 4% of baseline), diazoxide (85 +/- 5% of baseline) and anisomycin (90 +/- 4% of baseline) enhanced the FoC(60) as compared with the control group (53 +/- 7% of baseline, P < 0.0001). The enhanced FoC(60) induced by phorbol 12-myristate 13-acetate was abolished by calphostin C (52 +/- 5% of baseline) and 5-HD (56 +/- 3% of baseline), but not by SB 202190 (90 +/- 8%). The diazoxide-induced recovery of FoC(60) was attenuated by 5-HD (55 +/- 6% of baseline), but was not modified by calphostin C (87 +/- 5% of baseline) and SB 202190 (90 +/- 8% of baseline). The anisomycin-induced recovery of FoC(60) was abolished by calphostin C (61 +/- 9% of baseline) and SB 202190 (52 +/- 8% of baseline), but not by 5-HD (88 +/- 6% of baseline). In conclusion, PKC activation, opening of mitoK(ATP) channels and p38 MAPK activation in early reoxygenation induced the postconditioning of human myocardium, in vitro. Furthermore, PKC activation was upstream of the opening of mitoK(ATP) channels; p38 MAPK acted on PKC. Therefore, mitoK(ATP) and p38 MAPK seemed to be involved in two independent pathways.

Isoflurane protects cardiomyocytes and mitochondria by immediate and cytosol-independent action at reperfusion

BACKGROUND AND PURPOSE

The volatile anaesthetic isoflurane protects the heart from ischaemia and reperfusion (I/R) injury when applied at the onset of reperfusion [anaesthetic postconditioning (APoC)]. However, the mechanism of APoC-mediated protection is unknown. In this study, we examined the effect of APoC on mitochondrial bioenergetics, mitochondrial matrix pH (pH(m)) and cytosolic pH (pH(i)), and intracellular Ca(2+).

EXPERIMENTAL APPROACH

Cardiac mitochondria from Wistar rats were isolated after in vivo I/R with or without APoC (1.4%-vol isoflurane, 1 minimum alveolar concentration), and mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential (DeltaPsi(m)), and oxygen consumption were assessed. In isolated cardiomyocytes and isolated mitochondria I/R injury was produced in vitro, with or without APoC (0.5 mM isoflurane). Intracellular Ca(2+), pH(m), pH(i) and DeltaPsi(m) were monitored with SNARF-1, TMRE and fluo-4, respectively. Myocyte survival was assessed when APoC was induced at pH 7.4 and 7.8. In isolated mitochondria oxygen consumption and ATP synthesis were measured.

KEY RESULTS

In vivo APoC protected against mPTP opening, slowed mitochondrial respiration and depolarized mitochondria. APoC decreased the number of hypercontracted cardiomyocytes at pH 7.4, but not at pH 7.8. APoC attenuated intracellular Ca(2+) accumulation, maintained lower pH(m), and preserved DeltaPsi(m) during reoxygenation. Isoflurane did not affect the regulation of cytosolic pH. In mitochondria, APoC preserved ATP production rate and respiration.

CONCLUSIONS AND IMPLICATIONS

At reperfusion, APoC inhibited mitochondrial respiration, depolarized mitochondria and acidified pH(m). These events may lead to inhibition of mPTP opening and, consequently, to preserved DeltaPsi(m) and ATP synthesis. This reduces intracellular Ca(2+) overload and cell death.

Phenylephrine induces early and late cardioprotection through mitochondrial permeability transition pore in the isolated rat heart

BACKGROUND

The aim of this study was to investigate the role of mitochondrial permeability transition pore (mPTP) in cardioprotection afforded by phenylephrine pretreatment in early and late phases.

METHODS

Rat hearts were isolated and perfused with Krebs buffer in Langendorff preparation and subjected to 30 min regional ischemia followed by 60 min of reperfusion. Phenylephrine as a selective α1-adrenoceptor agonist and atractyloside as a specific opener of the mPTP were used. Seven groups (n = 6) of rats were randomly studied: (I) control: surgical procedure was performed with no ischemia/reperfusion, (II) ischemia/reperfusion: hearts underwent regional ischemia/reperfusion, (III) early phenylephrine: phenylephrine (50 μM) was perfused for 5 min prior to ischemia/reperfusion, (IV) late phenylephrine: rats were treated with phenylephrine (10 mg/kg, i.p) 24 h prior to ischemia/reperfusion, (V) early phenylephrine+atractyloside: hearts were perfused with phenylephrine as in group III and then atractyloside (20 mM) 5 min before reperfusion for 20 min, (VI) late phenylephrine+atractyloside: hearts were treated with phenylephrine as in group IV and then received atractyloside (20 mM), 5 min before reperfusion for 20 min, (VII) atractyloside-IR group: hearts were perfused with atractyloside (20 mM) 5 min before reperfusion for 20 min.

RESULTS

Compared with ischemia/reperfusion group, perfusion of phenylephrine in early and late phases decreased myocardial infarct size (% of ischemia zone), reduced creatine kinase-MB (CK-MB) in the coronary effluent, and improved cardiac function. Administration of atractyloside abolished cardioprotective effects of phenylephrine in both early and late phases and returned infarct size, CK-MB and cardiac function to levels as seen in ischemia/reperfusion group.

CONCLUSION

These results suggest that administration of atractyloside as a specific opener of the mPTP abolishes phenylephrine-induced early and late cardioprotection in the isolated rat hearts.

Physiology and Pharmacology of Myocardial Preconditioning

Perioperative myocardial ischemia and infarction are not only major sources of morbidity and mortality in patients undergoing surgery but also important causes of prolonged hospital stay and resource utilization. Ischemic and pharmacological preconditioning and postconditioning have been known for more than two decades to provide protection against myocardial ischemia and reperfusion and limit myocardial infarct size in many experimental animal models, as well as in clinical studies (1-3). This paper will review the physiology and pharmacology of ischemic and drug-induced preconditioning and postconditioning of the myocardium with special emphasis on the mechanisms by which volatile anesthetics provide myocardial protection. Insights gained from animal and clinical studies will be presented and reviewed and recommendations for the use of perioperative anesthetics and medications will be given.

Polyphenol (-)-epigallocatechin gallate during ischemia limits infarct size via mitochondrial K(ATP) channel activation in isolated rat hearts

Polyphenol (-)-epigallocatechin gallate (EGCG), the most abundant catechin of green tea, appears to attenuate myocardial ischemia/reperfusion injury. We investigated the involvement of ATP-sensitive potassium (K(ATP)) channels in EGCG-induced cardioprotection. Isolated rat hearts were subjected to 30 min of regional ischemia and 2 hr of reperfusion. EGCG was perfused for 40 min, from 10 min before to the end of index ischemia. A nonselective K(ATP) channel blocker glibenclamide (GLI) and a selective mitochondrial K(ATP) (mK(ATP)) channel blocker 5-hydroxydecanoate (HD) were perfused in EGCG-treated hearts. There were no differences in coronary flow and cardiodynamics including heart rate, left ventricular developed pressure, rate-pressure product, +dP/dt(max), and -dP/dt(min) throughout the experiments among groups. EGCG-treatment significantly reduced myocardial infarction (14.5+/-2.5% in EGCG 1 microM and 4.0+/-1.7% in EGCG 10 microM, P<0.001 vs. control 27.2+/-1.4%). This anti-infarct effect was totally abrogated by 10 microM GLI (24.6+/-1.5%, P<0.001 vs. EGCG). Similarly, 100 microM HD also aborted the anti-infarct effect of EGCG (24.1+/-1.2%, P<0.001 vs. EGCG ). These data support a role for the K(ATP) channels in EGCG-induced cardioprotection. The mK(ATP) channels play a crucial role in the cardioprotection by EGCG.

Drugs mediating myocardial protection

The occurrence of myocardial ischaemia will result in either reversible or irreversible myocardial dysfunction. Even when revascularization is successful, some reperfusion injury may occur that transiently impairs myocardial function. Therefore, treatment should not only be directed towards prompt restoration of myocardial blood flow but measures should also be taken to prevent or alleviate the consequences of myocardial reperfusion injury. Over the years, various strategies have been developed. The present contribution reviews a number of these strategies focusing on pharmacological treatments that have been developed to address myocardial reperfusion injury.

Sevoflurane postconditioning converts persistent ventricular fibrillation into regular rhythm

BACKGROUND AND OBJECTIVE

Recent studies showed that ischaemic postconditioning converted persistent ventricular fibrillation to sinus rhythm. The influence of anaesthetic postconditioning on ventricular fibrillation has not yet been determined. In the present study, we studied the possible effect of sevoflurane postconditioning on persistent reperfusion-induced ventricular fibrillation in the isolated rat heart model.

METHODS

Isolated Langendorff-perfused rat hearts (n=80) were subjected to 40 min of global ischaemia and reperfusion. The hearts with persistent ventricular fibrillation (n=16) present after 15 min of reperfusion were then randomly assigned into one of the two groups: controls (n=8), reperfusion was continued for 25 min without any intervention, and sevoflurane postconditioning (n=8), rat hearts in the sevoflurane postconditioning group were exposed to sevoflurane at a concentration of 8.0% for 2 min followed by 23 min of reperfusion. As for the third group, the rest of the hearts were included in the nonpersistently fibrillating hearts group (n=64). Left ventricular pressures, heart rate, coronary flow, electrogram and infarct size were measured as variables of ventricular function and cellular injury, respectively.

RESULTS

Conversion of ventricular fibrillation into regular rhythm was observed in all hearts subjected to sevofluane postconditioning. Regular beating was maintained by all anaesthetic postconditioned hearts during the subsequent reperfusion. None of the hearts in the control group had normal rhythm at the end of the experiment. At the end of reperfusion, the coronary flow was increased in sevoflurane postconditioned hearts compared with the hearts that did not develop persistent ventricular fibrillation.

CONCLUSION

Sevoflurane postconditioning possesses strong antiarrhythmic effect against persistent reperfusion-induced ventricular fibrillation. Anaesthetic postconditioning may have the potential to be an antiarrhythmic therapy for reperfusion-related arrhythmias.

Desflurane-induced postconditioning of diabetic human right atrial myocardium in vitro

AIM

We tested the hypothesis that brief exposure to desflurane at the time of reoxygenation might be able to protect against hypoxia-reoxygenation injury in human myocardium from diabetic (insulin-dependent, ID; and non-insulin-dependent, NID) patients and non-diabetic (ND) subjects.

METHODS

The force of contraction (34 degrees C, stimulation frequency 1Hz) in the right atrial trabeculae was recorded during 30min of hypoxia followed by 60min of reoxygenation. Desflurane (at 3, 6 and 9%) was administered during the first 5min of reoxygenation. The force of contraction at the end of the 60-min reoxygenation period (FoC(60)) was compared in the study groups (means+/-SD).

RESULTS

In the ND group, desflurane at 3, 6 and 9% (FoC(60): respectively 78+/-10%, 84+/-4% and 85+/-12% of baseline) enhanced the recovery of FoC(60) compared with the ND-controls (53+/-7% of baseline; P<0.05). In the ID group, desflurane at 3% (61+/-4%) did not modify the recovery of FoC(60) compared with the ID-controls (54+/-6%), whereas desflurane at 6 and 9% (75+/-11% and 81+/-8%, respectively) enhanced the recovery of FoC(60)vs the controls (P<0.05). In the NID group, desflurane at 3% (57+/-5%) also failed to modify the recovery of FoC(60) compared with the NID-controls (52+/-10%), while desflurane at 6 and 9% (80+/-10% and 79+/-7%, respectively) enhanced the recovery of FoC(60)vs the controls (P<0.05).

CONCLUSION

Desflurane in vitro was able to postcondition diabetic (both ID and NID) human myocardium at 6 and 9%, but not at 3%.

Organ protection by volatile anesthetics in non-coronary artery bypass grafting surgery

The cardioprotective properties of volatile anesthetics have been widely demonstrated by numerous randomized studies and meta-analyses in the setting of cardiac surgery, above of all during coronary artery bypass grafting procedures. Recently, conflicting results have been presented in cardiac non-coronary artery bypass grafting surgery. Unfortunately, despite the existence of a great number of studies comparing a total intravenous anesthetic regimen with an inhalational regimen, at present there are no randomized studies presenting data regarding mortality and important outcomes, such as myocardial infarction, in non-cardiac surgery. In this review we analyze and present the results of the most recent and important studies regarding anesthetic preconditioning in cardiac and in noncardiac surgery. Furthermore, we focus on the emerging data from animal experiments, discussing in particular the molecular mechanisms underlying anesthetic preconditioning.